This invention relates generally to compressors, and more specifically to compressor variable stator vane assemblies.
In gas turbine engines, air is pressurized in a compressor and channeled to a combustor wherein it is mixed with fuel and ignited for generating hot combustion gases. The hot combustion gases flow downstream into one or more turbine stages which extract energy therefrom for powering the compressor and producing useful work. At least some known compressors have a plurality of axial stages which compress the air in turn as it flows downstream. Each compressor stage may include a row of rotor blades extending radially outwardly from a compressor spool or disk, and a cooperating row of stator vanes extending radially inwardly from an annular casing.
To control performance and stall margin of the compressor, at least some known stator vane rows are variable for selectively adjusting an angle of the vanes relative to the air being compressed. At least some known variable stator vanes include a spindle which extends radially outwardly through a casing and to which is attached a lever. The lever in turn is pivotally joined to an actuation ring coaxially surrounding the compressor casing. At least some known variable stator vane assemblies join each of the actuation rings for different variable stages to a common beam pivotally joined to the casing at one end and joined to a suitable actuator at an opposite end. The actuator pivots the beam which in turn rotates the actuation rings connected thereto which in turn rotates the respective levers attached thereto for pivoting the corresponding stator vanes. However, an amount of stator vane pivoting may vary from stage to stage since the several actuation rings are joined to the common beam at correspondingly different pivoting lengths from the pivoting end of the beam. Moreover, the common actuation beam and/or interconnections between the beam and the actuation rings may increase the complexity and/or weight of some known variable stator vane assemblies, and therefore may increase costs and maintenance.
Because gas turbine engines sometimes operate over a range of output power, the operation of the compressor may be correspondingly scheduled for maximizing efficiency of operation without undergoing undesirable aerodynamic stall. Vane scheduling is controlled by the kinematic motion of the levers, actuation rings, and actuation beam. However, at least some known variable stator vane assemblies may be limited to unidirectional tracking of the stator vanes, which may result in a compromised schedule of the stator vanes. Moreover, once at least some known variable stator vane assemblies are configured for a predetermined schedule, it may be difficult and costly to adjust the schedule.